Electrophotographic printing processes generate toned images upon the surface of a photoreceptor drum or belt surface corresponding to the exposure pattern produced by a raster output scanning (ROS) system. The toned image is then subsequently transferred from the photoreceptor surface to either an intermediate transfer medium or the final imaging substrate, depending upon the specific printer embodiment. Residual toner may exist on the photoreceptor surface after this transfer process, which is typically removed via an electrophotographic cleaning subsystem. After this cleaning process, toner may still remain on the photoreceptor drum or belt according to the efficiency and condition of the cleaning station. In addition, defects may occur on the surface of the photoreceptor drum or belt due to scratches or wear by recording medium or the like. Such excess toner and defects may cause a loss in quality of images exposed on the photoreceptor surface. During these phases of the electrophotographic processes, inspection of the toner image existing on the photoreceptor drum, or residual toner layers occurring either after the transfer station or after the cleaning station, or inspection of the photoreceptor surface itself, may be applied to predict image quality performance of the process.
Detection of image quality issues on a printed page has been described in U.S. Pat. No. 6,819,352, in which sensor arrays are applied to capture 2-D images from the final print. A print is scanned to provide input for image uniformity adjustment
Raster input scanning systems have been described for use in multifunction devices to scan a toned image on the photoreceptor surface to render a digital input file, and may be used to achieve high resolution capability and speed. For example, U.S. Pat. Nos. 4,294,534, 4,345,835 and 4,376,576 disclose such multifunction image processing systems having a collection rod that senses the presence or absence of light beam reflected by a photoconductive surface and provides an analog image signal representative of a developed image scanned.